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<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Set 实践</title>
  </head>
  <body>
    <script>
      let arr = [1, 2, 3, 4, 5, 4, 3, 2, 1]
      let arr2 = [4, 5, 6, 5, 6]
      //1. 数组去重
      //   let result1 = [...new Set(arr)]
      //   console.log(result1)
      //2. 交集
      // 第一种
      // let result = [...new Set(arr)].filter(item => {
      //   let s2 = new Set(arr2) // 4 5 6
      //   if (s2.has(item)) {
      //     return true
      //   } else {
      //     return false
      //   }
      // })
      // console.log(result)
      // 第二种
      // let result2 = [...new Set(arr)].filter(item => new Set(arr2).has(item))
      // console.log(result2)

      //3. 并集
      //   let union = [...new Set([...arr, ...arr2])]
      //   console.log(union)

      //4. 差集
      // let diff = [...new Set(arr)].filter(item => !new Set(arr2).has(item))
      // console.log(diff)
    </script>
  </body>
</html>
